Oil burner control system



Oct. 15, 1940. A, BAAK 2,217,886

OIL BURNER CONTROL SYSTEM Filed April 1, 1938 H CLOSES BEFORE C OPENS ON HEATING H OPENS BEFORE 0 0,055 ON comma INVENT R Albert Baclk.

ATTORN EY Patented Oct. 15, 1940 UNITED STATES PATENT OFFICE 01L BURNER CONTROL SYSTEM Albert E.-Ba ak, Minneapolis, Minn, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application April 1, 1938, Serial No. 199,500 6 Claims. (01. 15 a -2s) The invention relates generally to automatic control systems for oil burners, and more specifically to an automatic oil burner control system having certain features of safety whereby dangers due to failure of ignition are minimized.

. In certain types of control systems now in use it is the practice to provide a fuel pump or valve to control the delivery of fuel to the nozzle of the burner, and an igniter for igniting the fuel so delivered. The fuel delivery means and the ignition means are energized by a control instrument, such as a room thermostat, on a, call for heat and after a predetermined time interval or I after combustion has occurred an ignition switch is operated to break the circuit to the igniter while the fuel delivery means continues to function. After the room thermostat has become satisfied it will deenerglze the fuel delivery means after which the ignition switch will reclose and n the system will be in a condition to restart under the control of the room thermostat.

If, in a system of the above type, the ignition switch should stick in open position while the system is running or for some other reason should fail to reclose after the fuel delivery means is deenergized by the room' thermostat, a subsequent call for heat by the room thermostat would energize the fuel delivery means, but due to the open ignition switch the ignition means would remain so deenergized. This means that raw fuel would be forced into the combustion chamber which would not be ignited, and should the ignition switch laterclose, due to a slight jar for example, the resultant spark might cause an explosion due to 85 the large quantity of unburned fuel present.

It is a prime object of this invention to provide a safety feature which will make such a condition as described above impossible.

A further object is to provide an oil burner 40 control system where the circuit to the ignition means must be closed before the burner motor can be energized.

Another objectis to provide an oil burner control system of the low voltage type wherein the 45 circuit for energizing the burner motor must first pass through a combustion switch by means of which the ignition means is energized.

These and other objects will become readily ap- 50 parent to those skilled-in the art as the following specification is read in the light of the accompanying drawing, in which Figure 1 is a circuit diagram of the control system of the present invention, with the parts 55 shown in the cold position, and

Figure 2 is the same circuit diagram with the parts shown in the running position.

The control system of this invention derives its power from the alternating current supply lines II and I2. One end of a primary winding l3 of 5 a step-down transformer.- I4 is connected by means of conductor 15 to the supply line l2. The other .end of the primary i3 is connected by means of conductor IE to a stationary contact II of a combustion switch generally indicated at I8. This combustion switch cooperates with a second stationary contact l9 which is joined by means of conductor 20 to a conductor 21 which, in turn, connects with the supply line(l4.

The combustion switch I is operated through a slip friction connection by means of a thermostat (not shown) which is mounted in the stack leading from the furnace-and comprises a flexible arm 22 and a rigid arm 23 connected together at one end. This switch is arranged so that on a decrease in temperature, the flexible arm 22 will engage its contact I! first, and a further decrease in temperature will cause it to flex and permit the rigid arm 23 to engage its contact II. This flexing of the arm 22 will also produce a wiping ac- '25 tion on the contact I! which will tend to keep it clean.

Step-downtransformer I4 is provided with a secondary winding 24 which is connected at one end by means of conductor 25 to a contact 26 of a '30 safety switch generally indicated at 21. This safety switch is shown more or less diagrammatically as being comprised of a bimetallic element 28 and an electric heater 29. Actually, it is intended that this switch shall automatically '35 break its contact 26 after the heater 29 has been energized for a predetermined length of time, and that it shall be necessary to manually reset it to close the contact 26. The details of the switch mechanism do not form a part of this invention and may take various forms, such for example as disclosed in the Denison Patent 1,958,081. The fixed end of the bimetallic element 28 is con-. nected by means of conductor 30 to a stationary contact 3| of a combustion switch generally indicated at 32. A second stationary contact 33 of combustion switch 32 is connected by means of conductor 34 to one end of the heater 2!, the

other end of which is connected by conductor 35 to the conductor 30. g

The combustion switch 32 is shown diagrammatically as being provided with a contact arm 30 which makes contact with the two stationary contacts II and 33. The contact arm 36 is to be operated through a slip friction connection by means of a thermostat located in the stack, and on an increase in temperature the arm 36 will close the hot contact 3| before the cold contact 33 is broken, and on a decrease in temperature the hot contact 3I will be broken before the cold contact 33 is made. This switch is shown diagrammatically and actually may take any one of a number of forms, one of which is disclosed in the Denison Patent 1,941,540. It might be pointed out also that both of the combustion switches I8 and 32'm-ay be operated by the same stack thermostat. The contact arm 36 is connected by means of conductor 31 to one end of a relay coil 38, the other end of which is connected by means of conductor 39 to a stationary contact 48. The other end of the secondary winding 24 is connected by means of conductor 4| to stationary contact 42. I

A room thermostat generally indicated at 43 comprises a bimetallic coil 44 to which are connected a flexible arm 45 and a rigid arm 46. On a decrease in temperature the flexible arm 45 makes contact first with the stationary contact 42, and a further decrease in temperature causes the arm 45 to flex and permit the rigid arm 46 to make contact with its stationary contact 40.

Relay coil operates an armature which is diagrammatically shown as a dotted line 41 in the drawing. Energization of the relay 38 will cause the armature 41 to move to the left and carry with it four switch arms 48, 49, 50, and 5|. A conductor 52 connects the relay coil 38 to the switch arm 48 which cooperates with a stationary contact 53 connected by means of conductor 54 to the bimetallic element 44 of the room thermostat. The switch arm 49 is connected by means of conductor 55 to the conductor'l6 and cooperates with stationary contact 56 which is connected by means of conductor 51 to the junction of the conductors 20 and 2|. Switch arm 50 cooperates with a stationary contact 58 which is connected by means of conductor 59 to the ignition means 68. The purpose of switch 58-56 is to prevent a feed back from line I2, conductor I5, primary winding I3, conductor I6, switch I1-23. conductor 6|, ignition means 68, conductor 59 to conductors 62 and 64,-motor 63, and conductor 65 back to line II. This condition would occur when switch I123 was closed and the thermostat 44 was satisfied. Ignition means 68 is also connected by conductor 6| to th switch blades 22 and 23 of the combustion s ch I8. Switch arms 58 and 5| are connected together by meansof conductor 62 and to burner motor 63 by means of conductor 64. Conductor 65 connects the burner motor to the supply line II. Contact arm 5| cooperates with a stationary contact 66 which is connected by means of conductor 61 to the other supply line I2.

Operation Figure 1 discloses the elements of the system in their cold position, that is the room thermostat is satisfied and the thermostat responsive to stack temperatures is cold and the system is, therefore, shut down. Assume now that the room begins to cool causing the bimetallic element 44 to move its switch arms 45 and 46 to the left. As a result of such cooling, switch arm 45 will first make contact with stationary contact 42, at which time no circuit will be closed due to the fact that the switch 40-46 will be open and the switch 48-53 will be open. The room will, therefore, continue to cool until the thermostat has caused engagement of the rigid arm 46 with its stationary contact 46. The relay coil 38 will now be energized if the primary I3 of the transformer I4 has been connected to the supply conductors I I I and. I2. This will depend upon the position of the blades 22 and 23 of the combustion switch I8. If these two switch arms have engaged the stationary contacts I1 and I9, a circuit will be completed from supply line I2 through conductor I5, primary winding I3, conductor I6, stationary contact I1, rigid arm 23, flexible arm 22, stationary contact I9, and conductors 28 and 2| back to the other supply line II. If such a circuit exists the primary of the transformer I4 will be energized and the relay coil 38 will therefore be energized through the following circuit: secondary winding 24 of transformer I4, conductor 4|, stationary contact 42, flexible arm 45, rigid arm 46, contact 40, conductor 39, relay coil 38, conductor 31, contact arm 36 of the combustion switch 32, cold contact 33, conductor 34, heater 29 of the safety switch 21, conductor 35, conductor 30, bimetallic element 28, contact 26, and conductor 25 back to the other side of the secondary winding 24.

Energization of the relay 38 will pull in the four arms 48, 49, 58, and 5|. Engagement of the arm 48 with its contact 53 will set up the following holding circuit for the relay coil 38: secondary winding 24, conductor 4|, contact 42, switch arm 45, bimetallic coil 44, conductor 54, contact 53,

switch arm 48, conductor 52, relay coil 38, conductor 31, switch arm 36, contact 33, conductor 34, heater 29, conductors 35 and 38, bimetallic element 28, contact 26, and conductor 25 back to secondary winding 24. It will be noted that this holding circuit does not pass through the switch contact 48 or rigid arm 46 of the thermostat 43 which means that the relay will be held in until the spring arm 45 breaks the circuit at its contact 42.

When switch arm 49 makes contact with the contact 56, it closes a circuit for the primary winding I3 which is independent of the contacts I1 and I9 of the combustion switch I8. This circuit is traced as follows: supply conductor I2,

conductor I5, primary winding I3, conductors I6 and 55, switch arm 49, contact 56, and conductors 51 and 2| to supply conductor II.

Engagement of contact 58 by switch arm 56 and contact 66 by switch arm 5| causes energization of both the ignition means and the burner motor. The ignition means is energized through the following circuit: supply conductor II, conductors 2| and 28, contact I9, flexible arm 22 of combustion switch I8, conductor 6|, ignition means 60, conductor 59, contact 58, switch arm 50, conductor 62, switch arm 5|, contact 66, and conductor 61 back to supply conductor I2. The burner motor is energized by the circuit from conductor I2, conductor 61, contact 66, switch arm 5|, conductor 64, burner motor 63, and conductor 55 back to the supply conductor II.

The conditions which obtain then when the room thermostat first makes its call for heat are that the relay 38 will be pulled in thus energizing the ignition means and the burner motor, the safety switch will be closed, and the combustion switch I8 will be closing its two contacts and the combustion switch 32 will have its cold contact 33 closed. Normally, under the above conditions, ignition will take place and the heat of the burner will pass up the stack to heat the thermostat which operates the two combustion switches. This will cause the contact arm 36 to engage the hot contact 3| and shunt out the heater :9 of the safety switch 21., This circuit w ll b as follows: secondary winding 24, conductor 4|, contact 42, switch arm 45, bimetallic --element 44, conductor 54, contact 53; switch arm &

48, conductor 52, relay coil 38, conductor 31, contact arm 36, hot contact 3|, conductor 38, bimetallic element 28, contact 26, and conductor 25 back to the other side of the secondary winding 24. A further increase in stack temperature will cause the contact arm 36 to break the cold contact 33 which definitely breaks the circuit connection to the heater 29. 4

The increase in stack temperature will also cause thecombustion switch l8 to leave its stationary contacts I! and i9. No change will occur when the rigid arm 23 separates from the contact due to the fact that this switch has already been shunted by the closure of the switch arm 49 with its stationary contact 56. However, disengagement of the spring arm 22 with the stationary contact I 9 will cause deenergization of the ignition means 60, and the burner motor will remain energized through the switch arm 5| and contact 66. The system will now be in its hot or. running position with the parts in the position shown in Figure 2.

The operation of the burner motor will cause heat to be supplied to the room which will warm up the room thermostat and cause it to first separate rigid arm 46 and stationary contact 40. This will produce no circuit change due to the fact that a holding circuit for the relay coil 38 has been set up through the switch arm 48 and contact 53. Further increase in room temperature will cause the flexible arm 45 to separate from stationary contact 42, which will deenergize the relay coil 38 and drop out the four switch arms 48. 49, 50, and 5|. As switch arm 5| "leaves its contact 86, the burner motor will become deenergized and the temperature in the stack will decrease which will cause the two combustion switches I8 and 32 to swing to the left and assume the positions shown in Figure l.

The above description of the operation of the system is the normal operation, but as pointedout in the objects, this invention is directed to certain features of safety to take care of abnormal conditions. The operation of these safety features will now be described. Assume, for example, that as the room thermo stat became satisfied dropping out the relay 38 and the stack temperatures commenced to drop that the combustion switch l8 became stuck and the flexible arm 22 did not make contact with its stationary contact l9. It will be noted that this is the switch through which the ignition means is energized and which breaks as combustion'is obtained to cut off the ignition means. If new the burner motor were energized on a callfor heat, there would be no spark to ignite the fuel and the raw fuel would be pumped into the furnace. With the present system, it can readily be seen that it is impossible now to energize the burner motor because after the relay coil 38 has been dropped out the primary winding l3 of'the transformer l4 depends for energization on a circuit which includes resilient arm 22 and its stationary contact l9. Therefore, if this switch or switch 23| I is not closed, there will be no power in the transformer and the relay coil 38 cannot be pulled in to-energize the burner motor. This feature which prevents the burner motor from being energized when no ignition is available is one of the main purposes of this invention.

Assume now that the combustion switch l8 had closed its circuits and that the room thermostat had pulled in the relay 38 to start the system in operation. It might occur that from some reason, although the circuit to the ignition means was closed, that the fuel failed to ignite. If such a condition occurred, there would be no combustion and hence the stack temperature would not increase so that the combustion switches l8 and 32 remain in the positions shown in Figure 1. In this case, the heater 29 for the safety switch 21 would ,not be shunted out o'f circuit and would eventually heat the thermostat 28 to the point where it would break the circuit at contact 26. This would dropout the relay 38 and the burner motor and ignition means would be shut down. It would then be necessary to locate the cause of the trouble and manually reset the safety switch. This feature of safety is customary in the art at present and is not a part of this invention.

Assume now that the room thermostat has called for heat and started the burner motor, that ignition has taken place, and that the system is running with the parts shown as in Figure 2. It might occur that due to dirt in the oil line or some other reason, the flame in the furnace should become extinguished while the room thermostat was still calling for heat and the burner motor was still operating. It will be remembered that at this time the combustion switch l8 will have caused separation of the flexible arm 22 and its contact l9 due to an increase in the stack temperature. Therefore, when the flame fails there can be no immediate spark to reignite it. In such a case'as this, the stack temperature will immediately begin to fall' andthe contact arm 36 will leave its hot contact 3| which will break the circuit to the relay 38 dropping out the switch arms 48, 49, 50, and 5| and therefore, deenergize the burner motor. The system will remain shut .down in this fashion until the contact arm 36 has closed its cold contact 33 and until the combustion switch l8 has caused the rigid arm 23 to engage its contact I! and the flexible arm 22 to engage its contact I9. The room thermostat will still be calling for heat and it will now pull in the relay 38 and attempt to restart the system in the normal manner. If the trouble which caused extinguishment of the flame has been corrected, the system will start up and operate normally, but if the trouble is still present the burner will not ignite. Pulling in the relay 38 will not cause an increase in stack temperature so that the heater 29 of the safety switch 2-1 will remain energized, and after a predetermined length of time cause the safety switch to open the circuit switches are still in the position shown in Figure 2, the burner motor cannot beenergized because of the fact that the switch arm 5| will not be in contact with its stationary contact 66. The system will remain shut down until the combustion switches have returned to the position shown in Figure 1 and it will be necessary to pull in the relay 38 through the heating element 29 of the safety switch 21 and to close the circuit to the If the power should. come on immediately while the combustion ignition means as in starting up under a normal operation. This is a very desirable feature because it will be remembered that when the combustion switches are in their hot position the circuit to the ignition means is broken, and therefore if it were possible to energize the fuel burner it would only act to pump the raw fuel into the furnace.

It will thus be seen that with the system of this invention, it is impossible at any time to cause energization of the burner motor without at the same time causing energization of the ignition means. This is the main feature of this invention and it is a very desirable result in producing automatic control systems for oil burners in that it minimizes the chances for an explosion due to the ignition of a relatively large quantity of raw fuel.

Modifications of this invention may occur to those skilled in the art for performing the same function, and it is therefore to be understood that I am to be limited not by the specific embodiment herein disclosed but rather by the scope of the appended claims.

I claim as my invention:

1. An electrical control system for liquid fuel burners comprising a high voltage supply, a step-down transformer having a primary winding and a secondary winding, a combustion responsive switch which is closed on lack of combustion and opened when combustion occurs, means for connecting said primary winding to said high voltage supply including said combustion responsive switch, an ignition means, means for connecting said ignition means to said'high voltage supply including said combustion responsive switch, a burner motor, means for connecting said burner motor to said high voltage supply including a normally open switch, a relay, means for connecting said relay to said secondary winding including a condition responsive switch, means for maintaining said relay energized independently of said combustion responsive switch, and means associated with said relay for closing said normally open switch.

2. An electrical control system for liquid fuel burners comprising a high voltage supply, a stepdown transformer having a primary winding and a secondary winding. a combustion responsive device, two switches operated thereby to closed position on lack of combustion and open position when combustion occurs, means connecting the primary winding to said high voltage supply including both of said switches, a first normally open switch for shunting both of said switches out of control, an ignition means, means for connecting said ignition means to said high voltage supply including one of said combustion switches and a second normally open switch, a burner motor, means for connecting said burner motor to said high voltage supply including a third normally open switch, a relay, means for connecting said relay to said secondary winding including a condition responsive switch, and means associated with said relay for closing said normally open switches.

3. A control system for fluid fuel burners comprising in combination, an electrical fuel feeding device, an ignition device for the fuel, a circuit for said electrical fuel feeding device, a relay which when energized closes said circuit to said fuel feeding device, first switch means responsive to the demand for heat in circuit with said relay, a circuit for said ignition device also closed upon energlzation of said relay, and ineluding a father switch means so arranged that the flow of current through said ignition device is independent of said first switch means except as said first switch means controls the operation of said relay, means for moving said second switch means to open position following the successful establishment of combustion, and means preventing the original energization of said relay by said first switch means unless said second switch means is in condition to pass current.

4. A control system for fluid fuel burners comprising in combination, a source of power, a transformer having primary and secondary windings, switch means, means connecting said primary winding across said source of power including said switch means, an electrical fuel feeding device, an ignition device for the fuel, a relay, a condition responsive device in circuit with said secondary winding for operatively energizing said relay, said relay upon energization establishing a circuit for said primary winding independent of said switch means, a circuit for said fuel feeding device and a circuit for said ignition device, the circuit for said ignition device including said switch means, and means for moving said switch means to open position following successful combustion.

5. A control system for fluid fuel burners comprising in combination, a source of power, a transformer having primary and secondary windings, switch means, means connecting said primary winding across said source of power including said switch means, an electrical fuel feeding device, an ignition device for the fuel, a relay, a condition responsive device in circuit with said secondary winding for operatively energizing said relay, said relay upon energization establishing a circuit for said primary winding independent of said switch means, a circuit for said fuel feeding device and a circuit for said ignition device the circuit for said ignition device including said switch means, means for automatically moving said switch means to open position to terminate ignition after said fuel feeding device has been energized and for automatically reclosing said switch means as'an incident to the termination of combustion.

6. A control system for fluid fuel burners comprising in combination, a source of power, a transformer havingprimary and secondary windings, switch means, means connecting said primary winding across said source of power including said switch means, an electrical fuel feeding device, an ignition device for the fuel, a relay, a condition responsive switch in circuit with said secondary winding for operatively energizing said relay, said relay upon energization establishing a circuit for said primary winding independent of said first named switch means, a circuit for said fuel feeding device and a circuit for said ignition device, both circuits being normally closed upon energization of said relay, the circuit for said ignition device including said first named switch means so arranged that the flow of current through said ignition device is independent of said condition responsive switch except as said condition responsive switch controls the operation ofsaid relay, means for automatically moving said first named switch means I to open position to terminate ignition after said fuel feeding device has been energized and for automatically reclosing said switch means as an incident to the termination of combustion.

ALBERT E. BAAK.

DISCLAIMER 2,217,886.Albert E. Baalc, Minneapolis, Minn. OIL BURNER CONTROL SYSTEM. Patent dated October 15, 1940. Disclaimer filed November 26, 1941, by the assignee, Minneapolis-Honeywell Regulator Company. Hereby enters this disclaimer to claims 3, 4, 5, and 6 of said patent.

[Ofiiez'al Gazette December 23, 1941.] 

